High intensity short arc lamp having an annular cathode shield



INVENTOR.

NORMAN c. BEESE I si;

N. C. BEESE HIGH INTENSITY SHORT ARC LAMP HAVING AN ANNULAR CATHODESHIELD Filed March 15, 1962 Nov. 5, 1963 ATTORNEY Unitcd States Patent()fiice 3,199,952 ?atented Nov. 5, 1963 3,109,952 HIGH INTENSITY SHGRTARC LAMP HAVING AN ANNULAR CATHGDE SHELD Norman C. Reese, Verona, Ni,assignor, by mesne assignments, to the United States of America asrepresented by the Secretary of the Navy Filed Mar. 15, 1962, Ser. No.13%,419 8 Claims. (1. 313207) This invention relates to electricaldischarge lamps and more particularly to high pressure, high current gasor vapor discharge short arc lamps which are constructed to providedesired acoustical resonance properties to be operative in opticalcommunication systems.

Lamps of the short arc type are known to the prior art and in generalare constructed of a material capable of withstanding high temperaturesand to provide a chamber for gases, such as argon, xenon, neon, etc.,alone or with mercury or other vapor additives, and within which arelocated electrodes for forming the arc.

Operation of short arc lamps on A.C. power in the audio-frequency rangeor on DC. power modulated by A.C. currents may be affected by soundvibrations produced within the gas chamber which are caused by thermallyinduced variations in gas pressure that result from changes in currentdensity in the arc. At certain critical frequencies, acousticalresonance of appreciable intensity may be built up by reflections fromthe bulb walls causing distortion or instability of the are which oftenresults in extinction of the arc. In lamps of generally cylindricalshape, the critical frequencies are primarily caused by sound energyreflected from the ends of the lamp structure while in lamps ofspherical shape the sound waves spread to the lamp walls and are thenfocused or directed back upon the arc to produce stability at theelectrodes.

The broad object of the invention is to provide a short are lamp whichis constructed in a manner to eliminate or minimize the effect ofdeleterious acoustical resonance on the arc stream when a resonantfrequency is used to operate or modulate the arc in order to permit thelamp to be used over extended periods of time.

Another object of the invention is to provide a short are lamp in whichprovision is made to prevent deleterious acoustical resonance which isdeveloped when the lamp is operated or modulated by a resonant frequencyfrom being reflected to the arc stream from the lamp walls.

Another object of the invention is to baflle or interrupt thedeleterious acoustical resonance developed when the lamp is operated ormodulated by resonant frequencies in order to prevent their interferingwith the arc stream.

Other and more detailed objects of the invention will become apparentfrom a better understanding of the invention, which may be had from theaccompanying drawings and description thereof.

FIG. 1 is a longitudinal sectional view of a short arc lamp showing oneembodiment of the invention for baffiing or interrupting acousticalvibrations and preventing em from being reflected from the bulb wallsback to the arc stream;

FIG. 2 is a longitudinal sectional view showing a modification of FIG.1.

Referring to FIG. 1, a gaseous discharge lamp of the short arc type withwhich the present invention is adapted to be used is generallydesignated by the reference 10 and is constructed of clear fused quartzand provides strong wall structure for withstanding the hightemperatures and pressures encountered during operation. The lamp isshaped to provide a central envelope section 12 and outer sections 14-14which respectively are equipped ped to form the anode and cathodestructures of the lamp. The components for each of the anode and cathodestructures are generally similar and differ only in the particulardesign of the anode electrode 15 and the design of the cathode electrode16. Since the components of the anode and cathode structures aregenerally similar, only the anode section will be described in detail toprovide an explanation of the manner of assembling the components and oftheir positional arrangement within the lamp 10.

The anode electrode 15 is constructed of tungsten and is mounted at theinner end of a tungsten rod 17 while a quartz collar 13 is positioned onthe rod adjacent its outer end and the outer end is secured in a quartzcoupling block 19. Another tungsten rod 29 has its inner end secured inthe opposite end of the coupling block 19 while its outer end extendsthrough a glass closure 21 to receive leads 22 by means of a connector23. Conductors in the form of thin molybdenum ribbons 24 are suitablysecured about the rod 20 and extend along the coupling block 19 and arewelded to the first tungsten rod 17 inside the collar 18. Afterassembling the anode components, as described, the outer section 14 ofthe quartz envelope is shrunk on to the coupling block 19 and collar 13to provide an integral structure; the end closure 21 is secured to thesection 14 by means of a quartz to glass seal indicated at 25.

The quartz coupling block and quartz collar arrangement for mounting thetungsten conductors 17 and 20 provide strength to the lamp structurewhile the conductor ribbons 24 provide for the transmission of heavycurrent loads from the leads 22 to the anode electrode 15. In thedrawing the similar components of the cathode are identified similarlyto those of the anode.

In FIGS. 1 and 2, the discharge are between the anode 15 and cathode 16is shown located off the geometric center of the central section 12 ofthe lamp and toward the cathode section 14 of the lamp. Although this isa preferred lamp construction, it will be understood that the detailedstructure of the invention, which will now be described, has utilitywith lamps in which the discharge arc has a different location.

According to the present invention, improvement in the performance ofthe above described lamp can be obtained by the provision of a baflle orshield which is indicated at 39 in FIG. 1. This component is formed of asiliceous material such as quartz and is in the form of an open endringlike or annular structure having a cylindrical end portion and aflared end portion. As shown in FIG. 1, the bafile or shield has oneedge 31 fixed to the lamp wall adjacent the inner end of the cathodesection 14' and its other edge 32 extending inwardly of the lamp centralsection 12 a short distance beyond the tip end of anode 15. Thus theshield surrounds or embraces the cathode electrode, a portion of theanode electrode and the arc stream therebetween providing an arrangementfor preventing the interference of reflected sound waves with the arcstream. A group of apertures 33 providing an apertured area are locatedin the cylindrical end portion 34 of the baflle or shield adjacent itsfixed edge 31 while the other end portion is flared at 35 toward thewall of the lamp central station 12. The apertures 33 and the flared endportion 35 of the baffle or shield permits the flow or circulation ofgas through the arc zone while the structure or body of the shieldfunctions to prevent the sound vibrations which are reflected from thewall of the envelope from disturbing the lamellar flow of gas throughthe arc zone.

The construction of the lamp of FIG. 2 is similar to that of FIG. 1 anddiffers thereover only in the details of the baflle or shieldconstruction. In FIG. 2 this component is indicated at 40 and has adifferent shape from shield 30. The shield 40 also has its inner edge 41fixed to the lamp wall adjacent the inner end of the cathode section 14'and its outer edge 42 positioned somewhat beyond the tip end of theanode 15. The apertured area is formed by a group of notches 43 in theend portion 44 of the bafile or shield and this end portion is flaredoutwardly as is the outer end, portion 45.

In the construction of FIGS. 1 and 2, the dimensions or relative size ofthe baflle or shield to that of the electrode structure are such as toprovide a space therewith and to position it relative to the lamp wallfor interrupting the reflected sound waves and thereby, when the lamp ismodulated, reduce or eliminate the resonant frequencies below thatencountered in normal use of the lamp. A lamp generally of the design ofFIG. 1 with the battle or shield having a diameter of the order of 1.8cm. across the arc zone was found, when modulated with audiofrequencies, to produce only slight disturbances below the resonantfrequency at about 11,800 c.p.s. and that me extinction occurred withabout 20 percent current modulation, while similar lamps not having thebaffle or shield, when modulated, reacted violently to resonantfrequencies at about 11,800 c.p.s. and cause arc extinction with 8 to 10percent current modulation. Also, in lamps not having the bafile orshield, it was observed that there were strong arc disturbances atresonant frequencies in the neighborhood of 9600 c.p.s., indicating thatthe bafile or shields were effective in reducing the intensityof severeresonant frequencies.

In the preferred embodiments of the invention, the shields 3t and 49 ofFIGS. 1 and 2, respectively, are shown mounted adjacent the cathodesection of the lamp but in some lamp constructions it may beadvantageous to mount the shields adjacent the anode section to extendtoward the cathode section and embrace the arc zone. The inventiontherefore is intended to cover all modifications of the embodimentsherein described which do not depart from the spirit of the invention.

I claim:

1. In an electric discharge lamp comprising a light transmissive centralgas chamber disposed between end electrode sections one containing anodecomponents including a conductor having an anode electrode disposedwithin the central chamber and the other containing cathode componentsincluding a conductor having a cathode electrode disposed within thecentral chamber and wherein the anode electrode and the cathodeelectrode 'are spaced to provide an arcing gap therebetween, the

improvement which comprises an annular shield within the central chamberand extending from the central chamber wall adjacent one of theelectrode sections toward the other electrode section, said shield beingof suflicient length to embrace the electrode of the one section and thearcing gap and to position its other end in alignment 1 with the tip endof the electrode of the other section and said shield having a diameterto provide an inner space with the electrodes for gas flow and an outerspace with the wall of the central chamber for sound vibrations.

2. An electric discharge lamp as in claim 1, further characterized bysaid one end of the annular shield being provided with an apertured areato permit'the circulation of gas through the inner space.

3. An electric discharge lamp as in claim 2, further characterized bysaid other end of the annular shield being flared outwardly.

4. An electric discharge lamp as in claim 1, further characterized bysaid annular shield having an apertured area adjacent its one edge andflaring from a generally central line toward both edges.

5. In an electric discharge lamp comprising a light transmissive centralgas chamber disposed between an anode end section containing anodecomponents including a conductor having an anode electrode disposedWithin the central chamber and a cathode end section containing cathodecomponents including a conductor having a cathode electrode disposedwithin the central chamber and wherein the anode electrode and thecathode electrode are spaced to provide an arcing gap therebetween, theimprovement which comprises an annular shield within the central chamberhaving one end secured to the central chamber wall adjacent the cathodesection and extending toward the anode section, said shield being ofsuflicient length to embrace the cathode electrode, the arcing gap and aportion of the anode electrode and said shield having a diameter toprovide an inner space with the electrodes for gas flow and an outerspace with the wall of the central chamber for sound vibrations wherebyinterference of sound vibrations with the arc gap is minimized.

6. An electric discharge lamp as in claim 5, further characterized bysaid one end of the annular shield being provided with an apertured areato permit the circulation of gas through the inner space.

7. An electric discharge lamp as in claim '6, further characterized bysaid other end of the annular shield being flared outwardly. v

8. An electric discharge lamp as in claim 5, further characterized bysaid annular shield having an apertured area adjacent its one edge andflaring from a generally central line toward both edges.

References Cited in the file of this patent UNITED STATES PATENTS2,716,713 Noel Aug. 30, 1955

1. IN AN ELECTRIC DISCHARGE LAMP COMPRISING A LIGHT TRANSMISSIVE CENTRALGAS CHAMBER DISPOSED BETWEEN END ELECTRODE SECTIONS ONE CONTAINING ANODECOMPONENTS INCLUDING A CONDUCTOR HAVING AN ANODE ELECTRODE DISPOSEDWITHIN THE CENTRAL CHAMBER AND THE OTHER CONTAINING CATHODE COMPONENTSINCLUDING A CONDUCTOR HAVING A CATHODE ELECTRODE DISPOSED WITHIN THECENTRAL CHAMBER AND WHEREIN THE ANODE ELECTRODE AND THE CATHODEELECTRODE ARE SPACED TO PROVIDE AN ARCING GAP THEREBETWEEN, THEIMPROVEMENT WHICH COMPRISES AN ANNULAR SHIELD WITHIN THE CENTRAL CHAMBERAND EXTENDING FROM THE CENTRAL CHAMBER WALL ADJACENT ONE OF THEELECTRODE SECTIONS TOWARD THE OTHER ELECTRODE SECTION, SAID SHIELD BEINGOF SUFFICIENT LENGTH TO EMBRACE THE ELECTRODE OF THE ONE SECTION AND THEARCING GAP AND TO POSITION ITS OTHER END IN ALIGNMENT WITH THE TIP ENDOF THE ELECTRODE OF THE OTHER SECTION AND SAID SHIELD HAVING A DIAMETERTO PROVIDE AN INNER SPACE WITH THE ELECTRODES FOR GAS FLOW AND AN OUTERSPACE WITH THE WALL OF THE CENTRAL CHAMBER FOR SOUND VIBRATIONS.